1. Field of the Invention
The present invention relates to a turbomolecular pump for use in a ultra-high vacuum system and a vacuum generation system required for manufacturing ICs, semiconductors and the like.
2. Related Art
A turbomolecular pump has a pumping section that includes multi stages of rotor blades having a shape similar to those of an axial flow compressor, and multi stages of stator blades alternatively arranged with the rotor blades.
There is known a case in which a new theoretical concept is applied to designing of the blades of this turbomolecular pump to provide effective compression capability and pumping speed not only in a free molecule flow region but also an intermediate flow region (cf. for example, Patent Document 1).
[Patent Document 1] Japanese Patent No. 3532653
FIG. 9 is a vertical cross sectional view of one example of a conventional turbomolecular pump. A rotor a is made up of an axial flow blade row that is composed of a large number of axial flow blades c arranged in multi stages and projecting outwards from a hub portion b.
Blades c of the axial flow blade row each are formed by a flat plate blade and one example of a development view in cross section in the circumferential direction of the axial flow blade row is shown in FIG. 10.
A blade row of a turbomolecular pump disclosed in the Patent Document 1 is made up of flat plate blades, as shown in FIG. 2 of this Patent Document 1.
The flat plate blade of this type has a small bending rigidity and therefore sudden vacuum break may take place in a vacuum portion on the upstream side, and if air inrush enters into a rotor section under this condition, the blades are greatly deformed and the adjacent rotor and stator blades resultingly collide with each other, which may cause a serious accident.
In order to prevent such collision due to air inrush, the rotor blades need to be thickened but the thickening of the rotors poses a problem of increasing stress on the inner circumference of a hub of the rotor.
Accordingly, it is an object of the present invention to provide a turbomolecular pump provided with rotor blades that solve those problems, have a high bending rigidity, prevent occurrence of excessive inner stress to the hub portion of the rotor, and have more excellent pumping performance than flat plate blades.